[llvm-dev] Hash of a module

Robinson, Paul via llvm-dev
Mon, 21 Dec 2015 17:29:27 -0000

| (canonicalizeOperands swaps arguments of an and and then ReassociateExpression
swaps them back).

That feels like its own bug, canonicalize and reassociate having different
opinions of canonical order.  Just saying.
--paulr

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Artur
Pilipenko via llvm-dev
Sent: Monday, December 21, 2015 9:11 AM
To: Russell Wallace
Cc: llvm-dev
Subject: Re: [llvm-dev] Hash of a module

There is a caveat here. I was experimenting with something similar and found
that this status is not always trustworthy. I fixed one bug in prune-eh. These
is also a bug in reassociate pass. It returns true with no change made on the
following instruction:
  %0 = and i64 %b, %a
It happens because it performs two distinct transformations which nullify each
other (canonicalizeOperands swaps arguments of an and and then
ReassociateExpression swaps them back).

This approach might work for your set of passes, but beware of the problem.

Artur

On 21 Dec 2015, at 19:59, Russell Wallace <russell.wallace at
gmail.com<mailto:russell.wallace at gmail.com>> wrote:

Yes, I'm running all the existing passes that I know how to run. I
didn't know they returned change-made. Thanks!

On Mon, Dec 21, 2015 at 12:36 PM, Artur Pilipenko <apilipenko at
azulsystems.com<mailto:apilipenko at azulsystems.com>> wrote:
Are you going to run some of the existing passes? Why can’t you just use the
returned change-made value from the passes?

Artur

> On 20 Dec 2015, at 15:43, Russell Wallace via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
>
> I want to run a bunch of optimizations, iteratively, that is keep running
until things stop changing (to make sure all optimization opportunities are
taken). As far as I know, there is no way to copy a module or compare modules by
value, so it occurs to me that a practical solution might be to take the hash
code of the module and see if that changes.
>
> A problem is that hash algorithms are designed to work on streams of bytes,
not compound objects.
>
> First attempt at a solution: iterate through all instructions in all
functions and hash the instruction kinds. I can think of some possible changes
that would fail to be captured by that.
>
> Is there any already known solution?
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20151221/89b68602/attachment.html>